a) Field of the Invention
The invention is directed to a telescope-type stereomicroscope which is outfitted with an objective and two magnification changers which are arranged downstream of the objective for selecting different magnifications while observing an object.
b) Description of the Related Art
In this type of construction of a stereomicroscope, two separate light channels are guided through one and the same objective in order to achieve the stereoscopic impression. Provided in sequence from the object are, first, the objective and, following that, in two beam paths which are oriented parallel to one another and which serve for separate observation by the left and right eye, a magnification changer which is generally afocal, a tube lens system, an image erecting system, and an eyepiece.
The sequence of the image erecting system and tube lens system may also be reversed depending on the construction of the stereomicroscope. Further, elements can be provided for reflecting illumination light and image information into and out of the beam path.
To an increasing extent, users of stereomicroscopes of this type of construction want the advantages of three-dimensional viewing combined with large visual fields and higher resolution. This enables an overview of an object and large object fields with high imaging quality and also detailed viewing of small object portions with high magnification without needing to change the objective when moving from one viewing mode to the other.
Further, a large free working distance between the object and objective is often desired so that the object can be manipulated with as little hindrance as possible.
Because of these demands, the microscope manufacturer is increasingly obliged to resolve the contradiction between decreasing the focal length of the objective in order to achieve higher resolution and ensuring large visual fields with a large free working distance.
One expedient for these conflicting requirements is to develop objectives in which the principal plane is advantageously positioned because a principal plane that is displaced in direction of the object results in an increased working distance. An objective of this kind is described in EP 1 369 729, for example.
However, this objective is relatively complicated to manufacture and therefore increases costs.